A Histochemical Investigation of Different Distribution of TSH Cells in Adenohypophsis of Female and Male Rats

Effect of estrogens on apoptosis in the pituitary of viscachas (Lagostomus maximus maximus)

Estrogens, acting through their receptors (ERα and ERβ), regulate cell turnover in the pituitary gland, influencing cell proliferation and apoptosis across various species. However, their role in pituitary processes in seasonally reproducing animals remains poorly understood. This study aims to investigate the influence of estrogens, through the expression of their specific receptors, on the apoptosis of PD cells in relation to sexual maturity, the reproductive cycle, and pregnancy in a seasonal reproductive rodent (Lagostomus maximus maximus). ERα and caspase-3-cleaved (CASP3c) immunoreactive (-ir) cells were identified through immunohistochemistry. Apoptotic cells were detected using the TUNEL technique, with quantitative analysis facilitated by image analysis software, alongside measurement of serum estradiol levels using radioimmunoassay The immunostaining pattern for ERα included nuclear (ERαn) and cytoplasmic (ERαc) staining. In male viscachas, ERα expression significantly increases from immature to adult animals, correlating with the rise in serum estradiol levels and a decrease in the percentage of apoptotic cells. During the gonadal regression period in adult males, a decrease in the number of ER-ir cells and serum levels of estradiol corresponds with an increase in the number of apoptotic cells. In females, serum levels of estradiol peaked during mid-pregnancy, coinciding with a significant decrease in the number of apoptotic cells in the PD. Simultaneously, the percentage of ERαn-ir cells reaches its maximum value during late pregnancy, indicating the need to maintain the protective action of this gonadal hormone throughout the extensive pregnancy in these rodents. Regional ERα receptor expression and apoptotic cells appear to be associated with distinct PD cell populations and their hormonal responses. Finally, elevated estradiol levels coincide with diminished apoptotic cells in the male reproductive cycle and during pregnancy, suggesting an antiapoptotic role of estradiol in this species.

Immunohistochemical and morphometric study of pituitary pars distalis folliculostellate cells of nonpregnant and pregnant viscachas

Pituitary folliculostellate cells (FSC) have several functions. Morphological, immunohistochemical and physiological characteristics of these cells have been reported for many mammalian species. There is little information, however, about the effect of pregnancy on FSC, particularly in wild animals. We conducted an immunohistochemical and morphometric study of the effect of pregnancy on FSC in viscacha, a seasonal breeder with a long gestation period. Immunohistochemistry and image analysis were used to measure the percentages of S-100-positive total, cellular, and colloidal areas and the number of FSC. In all groups studied, FSC were either isolated or arranged in small groups. These cells exhibited irregular nuclei, stellate shape, and cytoplasmic processes that delimited the follicles or contacted blood vessels. They expressed S-100 protein, which was localized both intracellularly (FSC) and extracellularly (follicular colloid). Some FSC were immunostained by anti-GFAP or anti-vimentin in the cytoplasm surrounding the nucleus and in the cytoplasmic processes, respectively. Morphometric parameters showed variation between nonpregnant and pregnant females. These variations were greatest during mid-pregnancy. We demonstrated that distribution of the FSC in pituitary pars distalis and expression of S-100 protein differ in nonpregnant and pregnant viscachas. Our findings suggest that FSC are involved in intrapituitary regulation of the hormone-secreting cells during pregnancy, probably by a paracrine mechanism.

The pituitary of non-pregnant and pregnant viscachas (Lagostomus maximus maximus): a comparative study by immunohistochemistry and morphometric analysis

The neuroendocrine hypothalamic-pituitary axis undergoes morphological and biochemical changes throughout gestation. In viscacha, pregnancy lasts approximately 154 days, and three stages can be described: early, mid- and late pregnancy. The aim of this work was to study the pituitary LH-gonadotrophs, FSH-gonadotrophs, somatotrophs, corticotrophs and thyrotrophs of non-pregnant and pregnant adult viscachas by immunohistochemistry and morphometric analysis. Immunopositive percentage area (%IA), cell percentage in the pars distalis (%PDC), number of cells per reference area (n°cell/RA), and major cellular (MCD) and nuclear (ND) diameters were analyzed. The different cell populations showed a well-defined morphology, immunolabeling patterns and regionalization in the pars distalis (PD). In the early pregnancy of animals the morphometric analysis demonstrated that %IA, %PDC and n°cell/RA increased in the FSH-gonadotrophs and decreased in the somatotrophs in relation to non-pregnant animals. In mid-pregnancy, there was an increase in %IA, %PDC, and n°cell/RA of LH-gonadotrophs, FSH-gonadotrophs, somatotrophs, and thyrotrophs. The MCD of LH-gonadotrophs and FSH-gonadotrophs increased. In late pregnancy, the %IA, %PDC and n°cell/RA of LH-gonadotrophs, FSH-gonadotrophs, somatotrophs and corticotrophs decreased whereas the values of the thyrotrophs remained constant. The MCD of LH-gonadotrophs, FSH-gonadotrophs and corticotrophs decreased. No significant changes were observed in the ND of the studied cell types. In conclusion, this work provides evidence for histological and morphometric changes in the different cell types of the pituitary PD in viscachas during pregnancy, probably according to the requirements of this physiological stage.

Anterior pituitary pyroglutamyl peptidase II activity controls TRH-induced prolactin release

Ecto-peptidases modulate the action of peptides in the extracellular space. The relationship between peptide receptor and ecto-peptidase localization, and the physiological role of peptidases is poorly understood. Current evidence suggests that pyroglutamyl peptidase II (PPII) inactivates neuronally released thyrotropin-releasing hormone (TRH). The impact of PPII localization in the anterior pituitary on the endocrine activities of TRH is unknown. We have studied whether PPII influences TRH signaling in anterior pituitary cells in primary culture. In situ hybridization (ISH) experiments showed that PPII mRNA was expressed only in 5-6% of cells. ISH for PPII mRNA combined with immunocytochemistry for prolactin, beta-thyrotropin, or growth hormone, showed that 66% of PPII mRNA expressing cells are lactotrophs, 34% somatotrophs while none are thyrotrophs. PPII activity was reduced using a specific phosphorothioate antisense oligodeoxynucleotide or inhibitors. Compared with mock or scrambled oligodeoxynucleotide-treated controls, knock-down of PPII expression by antisense targeting increased TRH-induced release of prolactin, but not of thyrotropin. Similar data were obtained with either a transition-state or a tight binding inhibitor. These results demonstrate that PPII expression in lactotrophs coincides with its ability to control prolactin release. It may play a specialized role in TRH signaling in the anterior pituitary. Anterior pituitary ecto-peptidases may fulfill unique functions associated with their restricted cell-specific expression.